1. Field of the Invention
The present invention relates generally to a rubber hose and particularly to such a rubber hose suitable for a fuel transporting line in an automotive engine room where the hose connects metal pipes.
2. Discussion of Prior Art
Referring to FIG. 2, there is shown a conventional rubber hose 104 for an automotive fuel line. The rubber hose 104 has a laminated-tube structure consisting of an inner rubber tube 101 having gasoline resistance (or resistance to gasoline), a reinforcing fiber layer 102 and an outer rubber tube 103 having weather resistance. Referring further to FIG. 3, a pair of opposite ends of the rubber hose 104 are fitted onto respective metallic pipes 105 and the fitted ends of the rubber hose 104 are tightly fastened to the metallic pipes 105 with the help of respective fastening bands 106.
Recently, the automobile technology has been largely developed. In consequence, automotive fuel such as gasoline is subjected to high pressure and high temperature for the purpose of regulating exhaust gas. Additionally, the automotive engine room is subjected to an extremely wide temperature variation from lower than -40.degree. C. to higher than 100.degree. C. Gasoline transported through the high temperature engine room tends to be oxidized due to the heat. The gasoline containing peroxides developed due to such heat, is called "sour gasoline". The sour gasoline adversely influences the rubber hoses transporting the fuel. Thus, nowadays, rubber hoses for an automotive fuel line are required to have more excellent properties, so that the hoses can be used in a satisfactory manner under severe conditions. The rubber hoses of the above-indicated type that have an inner rubber tube formed of a widely used polymer resistant to gasoline, cannot be used in automotive vehicles any longer.
Furthermore, gasoline or oil is a limited resource and the resource is expected to be drained out in the future. For coutermeasuring such situation, alcohol may be used as automotive fuel in the form of a mixture with gasoline. However, alcohol is erosive to rubber. In the situation, therefore, there will be needed rubber hoses having an inner rubber tube resistant to alcohol.
In view of the foregoing, it has been recommended that the inner rubber tube of rubber hoses be formed of fluorine-contained rubber (hereinafter referred to as "FKM"), because FKM has excellent heat resistance and sour-gasoline resistance (resistance to sour gasoline). However, FKM suffers from problems of low cool resistance (resistance to low temperature) and high cost of manufacture.
In the above-mentioned background, another rubber hose is available at present, which has a double-layered inner rubber tube consisting of a comparatively thin inner layer formed of the above-indicated FMK and an outer layer formed of a material having excellent low temperature resistance, such as hydrin rubber or acrylonitrile-butadiene rubber (NBR) (specifically, NBR which contains a comparatively small proportion of acrylonitrile and accordingly is excellent in low temperature resistance). However, this rubber hose has the problem of high cost of manufacture, and other problems.
Moreover, there has been developed a polymer blend (complex polymer) consisting of acrylic rubber and fluorine-contained resin, which has excellent sour-gasoline resistance comparable to that of FKM and costs lower than FKM. Since containing a resin, however, the polymer blend exhibits a comparatively high hardness after being cured. In the case where the polymer blend is used for forming an inner layer of an inner rubber tube of rubber hoses, the produced hoses have the problem of low elasticity. Furthermore, the inner layer formed of the blend polymer in question is not bonded with sufficient bonding strength to an NBR-based outer layer of the inner rubber tube, since the polymer blend is not vulcanized with high bonding strength to NBR. Japanese Patent Application laid-open under Publication Number 62(1987)-278395 proposed to add epoxy resin, silica or magnesium oxide to NBR for improving the bonding strength by vulcanization at the interface between the inner and outer layers of the inner rubber tube. However, even the thus produced rubber hoses have a tendency to be peeled at the interface in question during use.